1. Field of the Invention
The present invention relates to a sheet folding apparatus for folding a sheet-shaped recording medium, a sheet processing apparatus having this sheet folding apparatus and which conducts saddle stitch binding and the like, and an image forming apparatus such as a photocopier, printer, facsimile device and printer having such sheet folding apparatus or sheet processing apparatus.
2. Description of the Background Art
In an image forming apparatus such as a photocopier, printer, facsimile device and printer, an image is formed by visualizing a latent image carrier such as a photoconductive drum or photoconductive belt with a development agent such as a toner and transcribing this to a recording medium (as a matter of convenience, this is hereinafter represented as paper or a sheet).
In addition to a case of discharging only a single sheet having an image formed thereon from the image forming apparatus, there are cases where a plurality of sheets having an image formed thereon are bundled and collated in a required number of copies, fastened and bound with a stapler and thereafter discharged from the image forming apparatus, and a sheet post-processing apparatus or finisher is used as such a device.
With this kind of sheet post-processing apparatus, the sheets to be discharged from the image forming apparatus are sequentially received in an inclined intermediate tray, and the end edge of sheets in the width direction is aligned with a jogger fence or the like and the end edge of recording sheets that slid off to the lower end side of the intermediate tray is aligned by being pressed against a stopper or the like, respectively. Then, the end edge of sheets is subject to binding processing with a stapler, and the bundled sheet group is discharged to the discharge tray.
Conventionally, a configuration of providing a pawl for scooping the lower end of sheets to the transport belt for transporting the sheets housed in the intermediate tray, scooping the sheets in conjunction with the movement of the transport belt and transporting such sheets to the position of a discharge roller in order to discharge the bundled sheet group to the discharge tray after performing such binding processing is proposed in the gazette of Japanese Patent Laid-Open Publication No. H8-137151.
Meanwhile, as a method of sheet post-processing, in addition to the method of performing binding processing with a stapler to the end edge of sheets as described above, for instance, a saddle stitching method where the end edge is not bound and the center portion of the discharged sheets in the discharging direction is bound, and a middle folding method of folding the sheets at the saddle stitched position are also proposed in the gazettes of Japanese Patent Laid-Open Publication No. 2001-19251, Japanese Patent Laid-Open Publication No. 2001-206629 and Japanese Patent Laid-Open Publication No. 2002-167120.
Incidentally, in the configuration of the sheet post-processing apparatus which binds the end edge of sheets, a bundle pressing means for preventing the bulging of end edges; that is, a transport auxiliary rotative member having a wing member capable of pressing the surface of sheets is provided to a position facing the stapler; in other words, at a position where the end edges of sheets that slid off toward the stopper collide, in order to prevent the defective transport of sheets when the end edges of the bound sheets float.
Nevertheless, when re-transporting the sheets subject to binding processing, although the end edge of sheets in the width direction will be aligned with a jogger fence, since the end edge to be scooped with the pawl member; that is, the end edge on the back side of the transport direction of the sheets (hereinafter simply referred to as “back side end edge”) will merely be in a state of being mounted on the inner bottom face of the pawl member, the back side end edge of sheets will be disarranged depending on the number of sheets in relation to the size of the housing space in the inner bottom face. In particular, when binding via saddle stitching or middle folding, if the back side end edge of sheets becomes disarranged, misalignment of the end edge of the sheet bundle after the binding will become noticeable, and the finish will result in an inferior appearance.
Meanwhile, with a sheet processing apparatus having this kind of saddle stitching or middle folding function, the half folding of the sheet bundle is conducted by extruding with a folding plate the bound portion of the sheet bundle in which the center portion thereof was bound, and making a fold line by passing therethrough a pair of folding rollers provided in the moving direction thereof. When binding with this kind of saddle stitching, it is important that the folding position by the folding roller and the binding position coincide accurately, and that the folding position is not misaligned obliquely, which are also the strong demand of users.
Thus, in order to meet such demand, for instance, Japanese Patent Laid-Open Publication No. 2001-206629 discloses a configuration of aligning the sheet bundle, thereafter performing binding processing to 2 locations in the width direction thereof, and further hooking the leading edge of the folding plate to the binding needle and pressing it into a folding roller nip. Further, Japanese Patent Laid-Open Publication No. 2002-167120 discloses a configuration of providing, in order to determine the folding position, a stopper in the transport direction, and providing an alignment mechanism capable of moving in the width direction.
Nevertheless, with the configuration of these background arts, since a position in which the fold line will not become misaligned obliquely is set theoretically, there are cases where the fold line will become misaligned during the actual operation. This occurs because sheets that are cut into standard sizes are not a perfect rectangle.